Laundry on Scotland tour

We had laundry done for us in Oban at the tour hotel. There was also a laundromat in Inverness that was not far from the hotel to do it yourself. Some of our group did that.

I can't speak for the Scotland tour, however...
On the 3 RS tours we've taken, they will usually mention on intro day which days are ideal laundry days. Your tour guide will be able to tell you if it's a self-serve or drop off laundromat or if it's hotel service laundry. They'll never suggest a laundry option that doesn't work in the timeframe you have on the tour.

Now, if you don't follow their suggestions, and do your own thing, you could run into time issues.

Theres a drop off laundry in Oban on a backstreet ,they just weigh your stuff for price. Good folk they even let us leave our power banks to charge last summer.
In Inverness theres a laundry about 150 yds on the outbound side of the Ness Bridge more or less opposite the Tesco

There's also one at Caol just outside Fort William open 6 days .

During our Scotland Tour, there was an opportunity to drop off or do our laundry in Inverness. We had the afternoon off in Inverness, so the guide told us where the laundry was- not far from the hotel. We paid to drop off our laundry and have them do it. We came back the next day (as we were two nights in Inverness) and picked it up. It was all folded too. It was worth the price. One couple on our tour, did their laundry at their self service machines, spending most of the afternoon there. We decided we would rather use our free time doing other things in Inverness, but what ever floats your boat.